In response to certain wavelengths of electromagnetic radiation (or “actinic radiation”), photochromic materials, such as indeno-fused naphthopyrans, typically undergo a transformation from one form or state to another form, with each form having a characteristic or distinguishable absorption spectrum associated therewith. Typically, upon exposure to actinic radiation, many photochromic materials are transformed from a closed-form, which corresponds to an unactivated (or bleached, e.g., substantially colorless) state of the photochromic material, to an open-form, which corresponds to an activated (or colored) state of the photochromic material. In the absence of exposure to actinic radiation, such photochromic materials are reversibly transformed from the activated (or colored) state, back to the unactivated (or bleached) state. Compositions and articles, such as eyewear lenses, that contain photochromic materials or have photochromic materials applied thereto (e.g., in form of a photochromic coating composition) typically display colorless (e.g., clear) and colored states that correspond to the colorless and colored states of the photochromic materials contained therein or applied thereto.
Upon exposure to actinic radiation (e.g., sunlight), the photochromic material typically is transformed from the unactivated (or bleached) state to the activated (or colored) state over a period of time that is referred to as an activation time. Correspondingly, when exposure to actinic radiation is halted (e.g., due to shielding of sunlight), the photochromic material typically is transformed from the activated (or colored) state to the unactivated (or bleached) state over a period of time that is referred to as a fade time. It is generally desirable that the activation time and the fade time associated with a photochromic material in each case be minimized. In addition, it is desirable that the fade rate associated with a photochromic material be substantially linear. With photochromic eyewear, such as photochromic lenses, a linear fade rate allows the wearer's eyes to adjust more smoothly and less noticeably to the wearer as the lenses transform from a colored to a bleached state.
The amount of a photochromic material required to achieve a desired optical effect when incorporated into a composition or article typically depends, at least in part, on the amount of actinic radiation that the photochromic material is capable of absorbing on a per molecule basis. The amount of actinic radiation that a particular photochromic material absorbs on a per molecule basis is quantitatively referred with regard to the molar absorption coefficient (or “extinction coefficient”) of the photochromic material. Photochromic materials having a relatively high molar absorption coefficient are more likely to transform from a closed-form to an open-form upon exposure to actinic radiation, than photochromic materials having a relatively lower molar absorption coefficient. Correspondingly, photochromic materials having a higher molar absorption coefficient may be used in lower concentrations in photochromic compositions and articles, than photochromic materials having a lower molar absorption coefficient, without compromising the desired optical effect.
In some applications, a photochromic material having a relatively high and desirable molar absorption coefficient may have limited solubility in the composition or material into which it is to be incorporated (e.g., a coating composition). As such, compositions or materials in which the photochromic material has low solubility, may be capable of having incorporated therein only a limited and relatively low amount of photochromic material. With a limited and relatively low amount of photochromic material incorporated therein, the resulting photochromic composition would have reduced photochromic properties (e.g., having reduced absorbance when fully activated), than if more photochromic material were capable of being incorporated therein. Accordingly, increasing the solubility of a photochromic material in a particular composition, such as a coating composition, may be desirable in some applications.
It would be desirable to develop new photochromic materials that provide a desirable combination of molar absorption coefficients, activation times, fade times and linear fade relative to comparable photochromic materials. In addition, it would also be desirable that such newly developed photochromic materials have improved solubility in certain compositions, for example coating compositions.